1. Field of the Invention
The present invention relates to a hybrid vehicle that is equipped with an internal combustion engine and an electric motor for driving the vehicle.
2. Description of the Related Art
In recent years, a hybrid vehicle which is equipped with both an internal combustion engine (hereinafter referred to as “engine”) and an electric motor (hereinafter referred to as “electric motor” or simply as “motor”) for driving the vehicle has been developed.
In particular, there have been developed a hybrid vehicle which is constructed such that a planetary gear mechanism capable of absorbing rotations of an engine and an electronic motor is interposed between the engine and the electric motor and a transmission with a torque converter being omitted so that the total length of the transmission can be reduced (refer to Japanese Laid-Open Patent Publication (Kokai) No. 2002-118903), and a hybrid vehicle which is combined with a continuously variable transmission (CVT) to efficiently run an engine and a motor, thus improving both the fuel economy and the driving performance (refer to Japanese Laid-Open Patent Publication (Kokai) No. 2002-171601).
FIG. 7 is a view schematically showing a driving system (mainly a transmission) of the hybrid vehicle disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-118903. As shown in FIG. 7, a planetary gear mechanism 2 is provided at the inlet of a transmission 1. The planetary gear mechanism 2 is a double pinion type, which is comprised of a sun gear 21, an inner pinion 22 which is engaged with the sun gear 21, an outer pinion 23 which is engaged with the inner pinion, a carrier 24 which supports the pinions 22 and 23, and a ring gear 25 which is engaged with the outer pinion 23.
The sun gear 21 is connected to a rotary shaft 3a of an engine 3, and a rotor 41 of an electric motor 4 is connected to the carrier 24. On the other hand, the carrier 24 can be connected to an input shaft 61 of a CVT 6 via a carrier clutch 51, while the ring gear 25 can be connected to the input shaft 61 of the CVT 6 via a ring gear clutch 52. A ring gear brake 53 is interposed between a transmission casing 11 and the ring gear 25. Further, the transmission casing 11 is provided with a stator 42 of the electric motor 4 such that the stator 42 is opposed to the rotor 41.
The CVT 6 includes a primary pulley 62 connected to the input shaft 61 and a secondary pulley 64 connected to the primary pulley 62 via a belt 63. An output shaft 65 of the CVT 6 is connected to the secondary pulley 64. It should be noted that the primary pulley 62 includes a movable sheave 62a and a fixed sheave 62b, and the secondary pulley 64 includes a movable sheave 64a and a fixed sheave 64b. 
Further, rotation of the output shaft 65 is transmitted to a differential gear 8 via a gear 66 fixedly installed on the output shaft 65, a counter gear 71 fixedly installed on a counter shaft 7, and a ring gear 81. This rotatively drives left and right wheel axles (wheel driving shafts) 9L and 9R via the differential gear 8.
The carrier clutch 51, ring gear clutch 52, and ring gear brake 53 are hydraulic friction engaging devices of a wet multi-disc type which is friction-engaged by a hydraulic actuator, and is friction-engaged by hydraulic fluid supplied from a hydraulic control circuit, not shown. As shown in Table 1, various power transmission states as shown in a nomographic chart of FIG. 8 are achieved by properly engaging and disengaging the clutches 51 and 52 and the brake 53.
TABLE 1OPERATIVE MODE OFCARRIERRING GEARRING GEARDRIVING SYSTEMCLUTCHCLUTCHBRAKE(a)ENGINE IS STARTED BYXX◯ELECTRIC MOTOR(b)POWER GENERATING WHENXX◯VEHICLE IS ATSTANDSTILL (P RANGE)(c)DRIVE BY ELECTRIC MOTOR◯XX(FORWARD, REARWARD)(d)DRIVE BY ENGINE◯◯X(e)DRIVE BY ENGINE AND◯◯XMOTOR(f)POWER GENERATING IN◯◯XDRIVING(g)ENGINE TORQUE INCREASEX→◯◯X(IN STARTING, AND LOWSPEED→INTERMEDIATE ORHIGH SPEED(h)REGENERATIVE BRAKING◯XX(AT LOW SPEED)(i)REGENERATIVE BRAKING◯◯X(AT INTERMEDIATE ORHIGH SPEED)(j)DRIVE REARWARD BY ENGINE◯X□X: UNENGAGED,◯: ENGAGED,□: FRICTION - ENGAGED
Specifically, in the case where the engine 3 is started by the electric motor 4, only the ring gear brake 53 is engaged while the carrier clutch 51 and the ring gear clutch 52 are unengaged (refer to Table 1(a)). Then, as shown in FIG. 8(a), running the electric motor 4 at a sufficient speed enables the engine 3 to be started. On this occasion, the rotational direction of the motor 4 is opposite to that of the engine 3. Of course, since the carrier clutch 51 and the ring gear clutch 52 are unengaged on this occasion, power is not transmitted to driving wheels.
Also, in the case where the electric motor 4 is run as a power generator for the purpose of charging while the vehicle is at a standstill, only the ring gear brake 53 is engaged while the carrier clutch 51 and the ring gear clutch 52 are unengaged (refer to Table 1(b)). Then, as shown in FIG. 8(b), if the engine 3 rotates the electric motor 4, the electric motor 4 functions as a power generator to generate power for charging. On this occasion as well, the rotational direction of the motor 4 is opposite to that of the engine 3. Further, of course, power is not transmitted to driving wheels.
In the case where the vehicle is driven by only the electric motor 4, only the carrier clutch 51 is engaged while the ring gear clutch 52 and the ring gear brake 53 are unengaged (refer to Table 1(c)). Then, assuming that there is no input from the engine 3 (i.e. the sun gear 21 is stopped), as indicated by a thick solid line in FIG. 8(c), if the electric motor 4 is rotated in the direction opposite to the rotational direction of the engine 3, forward driving torque is input to the CVT 6 to move the vehicle forward, and as indicated by a broken line in FIG. 8(c), if the electric motor 4 is rotated in the same direction as the rotational direction of the engine 3, rearward driving torque is input to the CVT 6 to back the vehicle.
On the other hand, in the case where the vehicle is driven by only the engine 3, the carrier clutch 51 and the ring gear clutch 52 are engaged while the ring gear brake 53 is unengaged (refer to Table 1(d)). Therefore, as shown in FIG. 8(d), the sun gear 21, the planetary carrier 24, the ring gear 25, and the input shaft 61 of the CVT 6 are directly connected to each other, i.e. rotated integrally with each other, and when only the engine 3 is run, forward driving torque is input from the engine 3 to the CVT 6 to move the vehicle forward.
Further, in the case where the vehicle is driven using both the engine 3 and the electric motor 4, the carrier clutch 51 and the ring gear clutch 52 are engaged while the ring gear brake 53 is unengaged as above (refer to Table 1(e)). Therefore, as shown in FIG. 8(e), the sun gear 21, the planetary carrier 24, the ring gear 25, and the input shaft 61 of the CVT 6 are directly connected to each other, i.e. rotated integrally with each other, and when the engine 3 and the electric motor 4 are run, forward driving torque is input from the engine 3 and the electric motor 4 to the CVT 6 to move the vehicle forward.
Further, in the case where power is generated using the electric motor 4 while the vehicle is running, the carrier clutch 51 and the ring gear clutch 52 are engaged while the ring gear brake 53 is unengaged as above (refer to Table 1(f)). Therefore, as shown in FIG. 8(f), the sun gear 21, the planetary carrier 24, the ring gear 25, and the input shaft 61 of the CVT 6 are directly connected to each other, i.e. rotated integrally with each other, and when the electric motor 4 is run as a power generator while the engine 3 is run, part of driving force of the engine 3 rotatively drives the electric motor 4 as a power generator, and the rest of the driving force of the engine 3 is input as forward driving torque to the CVT 6 to move the vehicle forward.
Further, in the case where starting using the electric motor 4 is desired to be avoided due to a low battery capacity, and in the case where torque from the engine 3 is desired to be increased e.g. in extremely low vehicle speed/high load starting (rapid climbing road starting), the ring gear brake 53 is disengaged, the ring gear clutch 52 is engaged, and the carrier clutch 51 is kept unengaged after the engine 3 is started (refer to Table 1(g)). As indicated by a broken line in FIG. 8(g), when power is generated using the electric motor 4, the force applied to the electric motor 4 serves as reactive force for engine torque to increase engine torque, so that the electric motor 4 and the engine 3 are controlled such that the ring gear 25 is rotated forward, and as a result, the vehicle can be started.
If the carrier clutch 51 is gradually engaged in this state, the vehicle running state can be changed to a normal running state, i.e. a running state in which the vehicle is run using the engine 3 (refer to FIG. 8(d)), a running state in which the vehicle is driven using both the engine 3 and the electric motor 4 (refer to FIG. 8(e)), or a running state in which the vehicle is run using the engine 3 while power is generated by the electric motor 4 (refer to FIG. 8(f)) as indicated by a solid line in FIG. 8(g).
If regenerative braking conditions (for example, an accelerator is off, or a brake is on) are satisfied when the vehicle is running at a low speed (using only the electric motor 4), the carrier clutch 51 is engaged while the ring gear clutch 52 and the ring gear brake 53 are unengaged (refer to Table 1(h)). Then, the electric motor 4 is run to generate power and the CVT 6 is controlled to a low gear side, so that as shown in FIG. 8(h), rotation of the input shaft 61 of the CVT 6 is transmitted to the rotor 41 of the electric motor 4 via the planetary gear mechanism 2, and regenerative braking is carried out such that driving energy is converted into power generating energy (energy which drives the electric motor 4 to generate power).
Further, if regenerative braking conditions (for example, an accelerator is off, or a brake is on) are satisfied when the vehicle is running at an intermediate or high speed (using only the engine 4, or using the engine 3 and the electric motor 4), the carrier clutch 51 and the ring gear clutch 52 are engaged while the ring gear brake 53 is unengaged (refer to Table 1(i)). Then, the electric motor 4 is run to generate power and the CVT 6 is controlled to a low gear side so that engine output can be decreased, so that as shown in FIG. 8(i), revolution of the engine 3 and rotation of the input shaft 61 of the CVT 6 are transmitted to the rotor 41 of the electric motor 4 via the planetary gear mechanism 2, and regenerative braking is carried out such that engine revolving energy and driving energy are converted into power generating energy (energy which drives the electric motor 4 to generate power).
Further, in the case where the vehicle is backed using an output from the engine 3, the carrier clutch 51 is engaged while the ring gear clutch 52 is unengaged, and further the unengaged ring gear brake 53 is brought into a friction engaged state (refer to Table 1(j)). If the ring gear brake 52 is friction-engaged and the CVT 6 is controlled to rotate the planetary carrier 24 in the opposite direction, the running state is changed from a state indicated by a chain line in FIG. 8(j) to a state indicated by a solid line in FIG. 8(j), and the planetary carrier 24 is rotatively driven in the opposite direction by engine revolution to back the vehicle.
According to the above-described prior art, however, the rotor 41 of the motor 4 is basically configured to constantly rotate even when the electric motor 4 is not operated. This causes energy loss, and heat is likely to be generated in the motor 4 and may affect peripheral parts. Further, due to e.g. the action of counter electromotive force when the motor 4 is controlled, the higher the motor rotational speed is, the higher is the battery voltage required for controlling the rotation of the motor 4.
In recent years, a high-voltage battery has been developed for a hybrid vehicle, but to obtain a sufficiently high battery voltage, a plurality of batteries has to be connected in series. This increases vehicle costs, and necessitates taking measures to cope with high voltages.
Of course, if the vehicle is configured to be driven mainly by the electric motor 4, a high battery capacity is accordingly required to unavoidably increase vehicle weight and costs, but if the vehicle is configured to be driven using mainly the engine 3 and using the electric motor 4 supplementary, a lower battery capacity suffices. In this case, it is preferred that the electric motor 4 is stopped when unnecessary, and is operated at as low speed as possible.